Electronic metronome



W. M. A. ANDERSEN sept. 19, 195o ELECTRONIC METRONOME 2 Sheets-Sheet 1Filed May 29, 1946 INVENTOR. wamww,

SWM.

SePt- 19, 1950 w. M. A. ANDERSEN 2,522,492

ELECTRONIC METRONOME Filed May 29, 3.946 2 Sheets-Sheet 2 n n l IN V ENTOR. 2e/se 9121. muwaw) Afro/iwf' vide an electronic circuit PatentedSept. 19, 1950 ELECTRONIC METRNOME Walther M. A. Andersen, Hartford,Conn., assignor to Crystal Research Laboratories, Incorporated,Hartford, Conn., a corporation of Connecticut Application May 29, 1946,Serial No. 673,1.99

`6 Claims. l

My invention relates broadly to metronomes and more particularly to animproved circuit and structure of metronome embodying electronicprinciples.

One of the objects of my invention is to provide fa novel circuitarrangement for a metronome Lby which a timed, visual and audibleindicationl may be produced. v

Another object of my invention is to provide a construction ofelectronic metronome in which no moving parts are used to control thetiming of audible signals.

Another object of my invention is to provide an electronic metronomeincluding a source of illumination within the instrument so that asimultaneous flash of light is produced with each audible beat.

Still another object of my invention is to proarrangement for metronomesin which the accuracyy oi beat repetition is exceedingly high and iscontrolled as to accuracy by the frequency of a domestic alterhatingcurrent power supply line. l y

Still another object of my invention is to provide a circuit arrangementembodying a grid- .controlled rectifier oi' the gaseous type tube suchas a thyratron or cold cathode type tube for controlling a combinedaudible and visual repeating indication.

:Still another object of my invention is to provide a construction cimetronome of the electronic type including means for controlling thenude of the audible ticks or beats to meet various conditionsencountered.

Still another object of my invention vis to provide an adjustableelectronic metronome in which the frequency of the repeated ticks orbeats may be readily controlled in an instrument which is extremelycompact in size and simple in manufacture on a mass production scale.

Other and further objects of my invention 'reside in an electronicmetronome and circuit arrangement therefore as set iorth lmore fully inthe specification hereinafter following by reference to the accompanyingydrawings in which:

Figure l is a perspective view of the metronome of my invention; Fig. 2is an elevational yview of the adjustable magnetic actuating means andthe sound-reproducing diaphragm of the audible responsive deviceemployed in the metronome of my invention; Fig. 3 is a side view of theadjustable magnetic actuator and soundreproducing diaphragm illustratedin Fig. 2; Fig. -4 is a transverse sectionalview taken'subbeat.y

"that maintenance problems stantially on line 4--4 of Fig. 2; Fig. 5 isa theoretical 4vievv illustrating the distribution of magnetic fluxthrough the audible responsive device in the metronome; Fig. 6 is aschematic diagram of one circuit arrangement employing the principles ofmy invention; Fig. 7 is a modied circuit arrangement of the metronome ofmy invention; Fig. 8 shows a further modified form of circuit embodyingthe principles of my invention and which may be employed. as a source oia sawtooth Wave form usable in the electronic art; and Fig. 9illustrates a cold cathode type of metronome circuit embodying myinvention.

My invention is directed to an electronic type of 4metronomeiorgenerating audible sounds accompanied by visual indications for thepurpose of `marking or measuring time both audibly and visually. Theelectronic metronome of my invention is valuable in the musical artwherein mechanical devices have heretofore been employed for producingaudible sounds to set the rhythm. lThe electronic metronome of myinvention contains no moving parts to control the timing of .audibleresponses, and includes a source of illumination which producesasimultaneous iiash of light to accompany each audible The instrumentcontains no parts subject to excessive yvvear or excessive servicing soare minimized. The frequency of the beat repetition rate is controlledby the frequency of the alternating current domestic power supply linefrom which the instrument is energized, and this frequency may be`adjusted within a wide range'of limits broad enough to cover all of therequirements of rhythmic coordination or 'in the training of groups ofstudents, etc.

The metronome of my invention comprises 'a grid controlled Agas-filledtype tube such as a thyratron or coldl cathode type tube in whichthepower supply is furnished from the domestic power line. The circuitarrangement of my inu vention is adaptable to both alternating currentand direct currentoperation. In the circuit of my invention, provisionis mede for dropping the vpower supply 'potential 'to a value suitableorexciting the cathode of the thyratron if a thyratron is used. Inalternating current applications of the circuit of my invention, thepower supply which is supplied to the thyratron by the line circuit isksuitably reduced through a transformer lfor energizing the cathode ofthe thyratron.

The circuit which is associated 'with the gridcontrolled rectierincludes input and output means wherein the input means includes amultiplicity of adjustable resistors, and the output means includes anaudible and visual indicating means in association with a basic timingcircuit consisting of a resistor and a condenser, and wherein theresistor and condenser constitutes a mutual coupling between the inputand output means. I further modify the visual indicating means byutilizing an auxiliary condenser and resistor for minimizing eiects ofvariations found in types of visual indicating lamps used in the circuitof my invention, and for compensating for such variations. Theadjustable resistors in the input means are selected in very specialvalue in relation to the values of the basic timing circuit consistentwith the mutual coupling means between the input and output means. Thevalues of the resistors in the input means are so selected that thecalibrations on the beat frequency dial of the metronome may be spreadin a predetermined desired manner for the gradual increase or decreasein the frequency of the audible beat. The value of the resistance andcapacity in the basic timing circuit are selected for the logarithmic orexponential decay of the cathode potential, whereas, the values of theresistors in the input means are selected so that, with variations ingrid potentials, a desired calibration can be achieved.

Referring to the drawings in detail, reference character i designates acabinet structure forming a housing for the components of the metronomeof my invention. The housing carries a calibrated scale 2 on the irontthereof having graduations indicated at 3 thereon for timing the beatswhich are reproduced by the metronome. There are limit stops i and 5 atopposite ends of the scale 2 between which the indicator or pointer 6 isadapted to be angularly moved under control of adjustment knob l. Theindicator or pointer 6 is formed from transparent material through whichthe calibrations 3 on scale 2 are readily visible and readable. Thepointer indicator 6 is movable counterclockwise to decrease thefrequency of the beats and is shifted clockwise to increase thefrequency of the beats.

I have shown in Figs. 2-5 the rear panel 8 oi the cabinet structurewhich may be secured by screw devices passing through apertures 8a inthe rear of the cabinet structure I. The rear panel 8 is apertured at 8bfor the passage of sound waves emanating from the diaphragm 9. Thediaphragm 9 is formed from balsa wood, which has been found to besuitable in reproducing the beats or ticks of the metronome. The balsawood diaphragm 9 is secured in position upon spacer member I which isfastened to the rear of the panel 8 by appropriate securing screwsrepresented at I I which extend through the panel 8 and securing stripI2. Spacer I0 is apertured as represented at I0a for the passage of thesound waves from diaphragm 9 through the apertures 8b in the rear panel8.

The securing strip I2 is screw-threaded for the passage of thescrew-threaded adjustment screw I4 which projects through the rear ofpanel 8 and is provided with the knurled adjustment head Ma. Theadjusting screw I4 engages the end of the strip I6 of magnetic material.The strip I6 extends transversely of the diaphragm 9 and is angularlybent toward the spacer member I0 and terminates in an angular securingbracket represented at I'I. The bracket I'I is suitably secured by meansci screw I8 to the rear panel 8 4 so that the strip I6 is spaciallyrelated to the rear of diaphragm 9.

The strip I6 carries substantially centrally thereof the magnetic anglemember I9 which is secured thereto by screw member 20. The magneticangle member I9 forms a pole piece on which the magnetic bobbin 2l iswound. The magnetic angle I9 terminates in the pole head I9a which isspaclally related to the armature member 22 which is carried by thebalsa wood diaphragm 9. The strip I5 of magnetic material is perforatedat IGa to provide a tongue IIib which extends substantially parallel tothe pole piece on which the magnetic bobbin 2| is wound and vterminatesin substantially the same plane as the pole head I9a in spacial relationto the armature 22.

The tongue I6b forms a magnetic return path for the lines of magneticflux which thread the pole head I9a, and the pole piece on which bobbin2i is wound, which lines of flux pass through armature 22 and throughthe magnetic strip I6. rlhus it will be seen that by turning knurledhead Ida of screw member I4 the magnetic bobbin and pole head I9@ andtongue IGZ; may be advanced toward or retracted from the armature 22 forcorrespondingly increasing or decreasing the volume of the tick or beat,thereby providing an adjustable metronome, not possible in structures ofthe prior art.

The securing screw 20, in addition to serving as a. fastening means forthe angle I9, also serves as a securing means for the angle member 23 towhich is fastened the panel 24 of insulation material. The panel 2dprovides mounting means for lugs 25 and 2'1 which serve as terminals forthe bobbin 2I which is connected in the electronic circuit of themetronome.

The circuit arrangement in which the magnetic bobbin 2I is arranged hasbeen illustrated in various forms in Figs. 6, 7, and 8.

Referring to Figure 6, the basic system comprises a grid controlledrectifier 28 (gas filled thyratron) in series with the coil of a speakerunit which may comprise any common type loud speaker, telephone headset, or electrical relay indicated generally at 29. The thyratronincludes cathode 28a, control grid 28h, anode 28c, and iilament 28d, theanode being connected to one side of the alternating current powersupply line 30 through switch 3|. The cathode 28a connects through theunit 29, and through the basic timing circuit 32 with the opposite sideof the power supply line 30, which may be the domestic 110V A. C. powerline. The basic timing circuit 32 consists of resistor 33 shunted bycondenser 34. The values of the components in the basic timing circuit32 are very critical, and the product of the values of the resistance 33and the capacity 34 must equal a time constant of .45 second. Across theline 30 is an adjustable tap resistance 35 and a fixed resistance 3Bconnected in series. The adjustable tap 35a is connected to the controlgrid 28h of the thyratron 28 through a resistance 31 adapted to limitthe iiow of current into the grid circuit. A filament heatingtransformer 38 is also provided to heat the lament 28d of the thyratron.The value of resistance 35 is 20,000 ohms i570, and the value ofresistance 31 is 910,000 ohms i20%, while the value of resistance 36 is6200 ohms r5%. The ratio of the value of resistance 36 to 35 is as 31 toand that ratio in conjunction with a time constant of .45 second, whichrepresents the product of the. values of components 33 and 34, gives adesirably spaced calibration for the metronome.

Capacitor `34 is connected in parallel with a resistance 33 and a glowtype (neon) lamp 39 or iilament type of lamp. The thyratron circuitincludes input means 30-35--36 and 31 and output means 29e-39. The inputand output means are coupled through the basic timing circuit 32 asshown. The operation of the vcircuit is as fol lows: When the switch 3|is closed and the thyratron filament y28d is heated to operatingcondition, on .the half cycle of A. C. potential, and when a positivevoltage is applied to the anode 28o of the thyratron 28, it will conductand a pulse of current will ow, charging the capacitor 34. This pulse ofcurrent vflowing through Athe unit 29 will cause the unit to emit anaudible tick or beat. Simultaneously with .the charging of the condenser34, the voltager thereon is .applied to ythe terminals vof the neon lamp39 which then glows.

As the cathode-anode voltage of the thyratron 28 reduces owing tocharging of the condenser 34 and the alternation of the A. C. voltage isapm plied to the plate 28e, a, vpoint is reached where the thyratron isextinguished. The condenser 34 discharges through the neon lamp 39 andresistance 33 until .a `voltage between thyratroncathode vand anodeagain is sufficient .so that for a positive cycle of voltage thethyratron again fires and the cycle is repeated.

During the period when :the condenser 34 is discharging, when .voltageacross the condenser is reduced suiliciently, the neon lamp 39 isextinguished. The `condenser continues to .diccharge through the shuntvresistance 33 only.

Adiustment of the voltage ,applied to the th-yra tron grid 28b by meansof the adjustable tap resistor Sii` determines the cathode-.anodevoltage required for .reiiring the thyratron, and thus determines `thektime delay between successive pulses. Thus the circuit provides meansfor creating both audible and visual signals at timed intervals.Inasmuch as the pulse occurs `when the anode 28e is positive, Ythedevice tends to repeatits pulsing in an integral number of half cyclesof the A. C. vwaves Supplying the system. And thus the precision of4repetition is controlled bythe precision of thepowerlineffrequencywhich is generally so accurate that synchronouselec-I tric clocks are continuously operated thereon. The basic timingof this system is kcontrolled by the resistance-capacitancecombination-3334, and the setting of the tap 35a onresistor 35.

In practice, theresistor 35 is a potentiometer having the calibratedLscales .shown in Fig. 1. While a, wide range of frequencies isobtainable, for musical work the range between 40 and 28 beats `perminute is preferred. This is obtained by proper choice of the timeconstant v33-34, and of yresistors 36 and 35,. Resistor 3,6 canfbe sochosen that a desired range is lcoveredfby the maximum excursion of thetap on resistance 35.

One undesirable `fea-ture of the Fig. v6 is that the ktiming andcalibration is influenced by the characteristics of the kneon lamp 39.In order tok overcome this objection the circuit of Fig. 7 is provided.

In Fig. 7 the basic circuit is `the same as that of Fig. 6 except thatthe neon lamp 33 is con nected in .series with a parallelresistancecapacitance combination 4-4.|. This network is connectedacross `condenser 34 as shown. Operation of the circuit involvingresistors 3.6-35-31. thyratron28,.speaker 2|. resistor 3,3k

and-condenser 34, is the same as described for Fig. 6. However, when acurrent pulse charges condenser 34, the voltage thereon causes the neonlamp 39 to glow for an instant while current through it chargescondenser 40. When condenser 40 charges sufficiently, the voltage acrossthe lamp 39 becomes so low that it will not maintain a discharge, and isthus .extinguished.

By this expedient, the current flow through the lamp 39 exists for asmall part of the time interval during which condenser 34 kisdischarging.. Inasmuch as the discharge current through the lamp 39occupies a small fraction of this total discharge current, variation oflamp characteristics have a minimum effect on the timing, and pulserepetition rate of the circuit.

.Between pulses, while the lamp 3S lis extinguished, the capacitor 43discharges through resistor 4l. It is kdesirable that the time constant40-4l be approximately the same as that of 33--40 for optimum operation.

Referring to Fig. 7, I have illustrated a further modified form ofmetronome circuit in which a thyratron 28 is employed utilizing anauxiliary grid 28e which is externally connected with the cathode 28dand interposed between the control rid 28h and the anode 28e. Thecathode circuit includes the speaker winding represented at 27interposed in series with the basic timing circuit 32. The speakerwinding 2! is illustrated as a general case for any type of device whichmay be magnetically excited at repeatedintervals under control ofthebasic timing circuit 32 and the associated condenser resistor circuit411-41 with the discharge lamp 39 interposed therebetween.

In Fig. 8 I have illustrated the circuitof my invention utilized as` agenerator of timed impulses of saw-toothed characteristic represented bythe curve 46. The thyratron circuit is arranged in a ymanner similar Atothe circuits described in connection with Figs. 6 and 7, except that thepower supply circuit 3B connects across potentiometer 43 whichdetermines the voltage impressed between the anode 28e of thyratronk28throughy reducing resistance 42 and the i'llamentary cathode 28d throughthe resistance 33 of the basic timing circuit 32. The control grid 28his connected through resistor 31 with adjustable tap 44 operating overpotentiometer 43. The lamentary cathode 28d is energized throughtransformer system 38, as yheretofore explained. The (S0-cyclealternating current supplied to the power supply terminals 33 isrectiiied by thyratron 2B and pulses of current delivered at terminals4.5 determined by the characteristics of the basic timing circuit 32. Bycontrolling the value ci resistor 33 and the value of condenser 34 a sawtooth wave of prede-v termined periodicity is delivered at terminals 45.

In Fig. 9 I have illustrated a circuit arrangement `for ra cold cathodetype of tube 4'! which includes cold cathode 41a, control grid 1b andplate 41o. Alternating current or direct current is applied at terminalsto the circuit ofthe cold cathode tube 4l between anode 41e and coldcathode 41a through the basic` timing circuit which includes resistor 33and condenser 34 and through theispeaker winding 2|.. The vpotentialdetermining circuit, including resistors `36 andk is arranged in Lshuntwith the power supply circuit .30 as. heretofore explained'. -The tap`35d connectsthrough resistors 3T -to control grid 41o of.`coldx=cathode tube 4J. The basic. timinglcircuit 32 is connected throughgaseous discharge tube 39 to the shunt-connected circuit containingcondenser 40 and resistor 4|. I have successfully used the type OA4Gtube for carrying out the functions of the circuit illustrated in Fig.9.

In the circuit of Fig. 6, consider that the switch 3| is closed, whichapplies alternating current power across the filament transformer 38,across 35-3B, and across the thyratron speaker unit 2| and the basictiming circuit 32 and the neon lamp 39.

Assume the filament 28d sufficiently heated on the rst positive halfcycle of A. C. power and the grid 28h will either be positive ornegative with respect to the cathode, or at most, a zero potential willexist between the grid 28h and the cathode Sa. The exact condition willdepend on the position of the tap 35a on the potentiometer 35. In anyevent the tube will on this first positive half cycle immediatelyconduct, feeding a heavy current through the speaker unit 2| causing itto tick and charging condenser 34 to some positive voltage with respectto ground. The peak of this surge will cause the neon lamp 39 to ash asmentioned before, but a charge of current will be left on condenser 34after the neon lamp 39 has extinguished itself.

On succeeding half cycles the cathode will be positive with respect tothe grid of the thyratron 28 and the tube will not again conduct untilthe charge across condenser 34 has leaked off suiciently to the resistor33 so that the bias is low enough to permit conduction. In Fig. '7, asomewhat more reiined circuit is depicted. The thyratron is of thescreen grid type and could conveniently be such types as the RCA 2050,RCA 2051, RCA 2D2l or RCA 2A4G types. It will be noted the net work40-41 is connected in series with neon lamp 39. This is so as tominimize the amount of current drawn by the neon lamp 39 so thatvariations in neon lamps will cause only a very slight variation in thecalibration. Net work 40-4I should have approximately the same timeconstant that net work 33-34 has.

A particular type of speaker has been developed for this instrumentwhich is convenient because of its extremely low cost and because theloudness of the tick can be easily adjusted. It will be noted that thecoil 2| is supported on a exible metal frame which is attached toanother frame made of wood or other suitable material. The adjustingscrew I4 pulls the coil 2| and polepiece |9a as close to the diaphragm 9with the armature 22 as is desirable, which causes a variation in theloudness of the tick. Connections are formed from the coil terminals26-21 to the cathode of the thyratron and to the net work comprising33-34 and ISU-4| and the neon lamp 3|. When a surge of current passesthrough the coil 2| the armature 22 is pulled up, causing the diaphragm9 to emit a sharp sound.

When a surge of current passes through the coil 2|, the magnetic eldthereby causes a mechanical force impulse on the armature 22. Thismomentary force exerted on the armature 22 causes the wood diaphragm 9to vibrate, giving a loud audible tick. Depending on the adjustment bymeans of the screw I4 of the gap space between the polepiece I9a andarmature 22, the tick may be made loud or soft as desired. As thisadjustment ismade the quality of sound is also varied. Adjustment can bemade so that during an impulse the armature can touch the polepiece I9a.This produces a loud metallic tick.

While I have described my invention in certain preferred embodiments, Irealize that changes. in detailed arrangement of the circuits may bemade and I intend no limitations upon my invention other than may beimposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. An electric system for producing audible sounds at a repetitive ratecomprising a gaseous discharge rectifier tube having a cathode, acontrol electrode and an anode, an alternating source of power, oneterminal of said power source being connected to said anode, anelectromechanical transducer connected in series with said cathode, atime constant circuit consisting or" a resistance and a capacitorconnected in parallel, said time constant circuit being connected inseries to said transducer, an electrical return connecting said timeconstant circuit to the other terminal of the alternatingsource ofpower, a potentiometer arrangement connected across the alternatingsource of power and a variable tap connected between said potentiometerand said control electrode.

2. An electric system for producing audible sounds at a repetitive ratecomprising a gaseous discharge rectifier tube having a cathode, acontrol electrode and an anode, an alternating source of power, oneterminal of said power source being connected to said anode, anelectromechanical transducer connected in series with said cathode, atime constant circuit consisting of a resistance and a capacitorconnected in parallel, said time constant circuit being rconnected inseries to said transducer, an electrical return connecting said timeconstant circuit to the other terminal of the alternating source ofpower, a potentiometer arrangement connected across the alternatingsource of power, a movable tap on said potentiometer connected to saidcontrol electrode, and a loading resistor disposed in said lastmentioned connection whereby a predetermined voltage is applied to saidcontrol electrode.

3. An electric system for producing rhythmic beats at a repetitive ratewhich comprises a gaseous discharge rectifier tube having a cathode, acontrol grid and an anode, an alternating source of power, one terminalof said power source being connected to said anode, an electromechanicaltransducer connected in series with said cathode, a time constantcircuit consisting of a resistance and a capacitor connected inparallel, said time constant circuit being connected in series with saidtransducer, a second gaseous discharge tube coupled to said timeconstant circuit, an electrical return connecting said4 time constantcircuit to the other terminal of the alternating source of power, apotentiometer arrangement connected across the alternating source ofpower, an adjustable tap on said potentiometer connected with saidcontrol electrode, whereby a predetermined voltage may be applied tosaid control electrode.

4. An electric system for producing rhythmic beats at a repetitive ratewhich comprises a gaseous discharge rectier tube having a cathode, acontrol grid and an anode, an alternating source of power, one terminalof said power source being connected to said anode, an electromechanicaltransducer connected in series with said cathode, a timeconstant circuitconsisting of a resistance and a capacitor connected in parallel, saidtime constant circuity being connected in seriesA with said-transducer,a second gaseous discharge tube coupled to said time constant circuit, asecond time constant circuit consisting of a capacitor and resistorconnected in series with said second discharge tube, whereby the amountof current `from said rst discharge tube through said second dischargetube is minimized, an electrical connection between said time constantcircuits and the other terminal of the a1- ternating source of power, apotentiometer arrangement connected across the alternating source ofpower, a variable tap on said potentiometer connected with said controlelectrode, whereby a predetermined voltage may be applied to saidcontrol electrode.

5. An electric system for producing rhythmic beats at a repetitive ratewhich comprises a grid controlled cold cathode tube having a cathode, acontrol grid and an anode, an alternating source of power, one terminalof said power source being connected to said anode, an electromechanicaltransducer connected in series with said cathode, a time constantcircuit consisting of a resistance and a capacitor connected inparallel, said time constant circuit being connected in series with saidtransducer, a second gaseous discharge tube coupled to said timeconstant circuit, a second time constant circuit consisting of acapacitor and resistor connected in series with said second dischargetube, whereby the amount of current from said first discharge tubethrough said second discharge tube is minimized, an electricalconnection between said time constant circuits and the other terminal oithe alternating source of power, a potentiometer arrangement connectedacross the alternating source of power, a movable tap on saidpotentiometer, a connection between said tap and said control electrodeand a resistor interposed in said connection, whereby a predeterminedvoltage may be applied to said control electrode.

6. An electric system for producing rhythmic beats at a repetitive ratewhich comprises a gaseous discharge rectier tube having a cathode, acontrol grid and an anode, an alternating source of power, one terminalof said power source being connected to said anode, an electromechanicaltransducer connected in series with said cathode, a time constantcircuit consisting of a resistance and a capacitor connected inparallel, said time constant circuit being connected in series with saidtransducer, a second gaseous discharge tube coupled to said timeconstant circuit, a second time constant circuit consisting of acapacitor and resistor connected in series with said second dischargetube, whereby the amount of current from said first discharge tubethrough said second discharge tube is minimized, an electricalconnection between said time constant circuits andthe other terminal ofthe alternating source of power, a potentiometer arrangement connectedacross the alternating source of power, a variable tap on saidpotentiometer connected with said control electrode, a resistor disposedin said connection whereby a predetermined voltage is applied to saidcontrol electrode and an adjusting screw for controlling the amplitudeof said sound reproducer.

WALTHER M. A, ANDERSEN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

